A paucity of information exists on the physiology and endocrinology of daily torpor. This thermoregulatory response may represent a physiological state intermediate between sleep and hibernation. A understanding of the physiological and endocrinological basis for daily torpor may lead to a better understanding of sleep and the mechanisms that enable the gradual, controlled entry of mammals into hibernation. This proposal seeks to characterize via computerized radiotelemetry the induced (food rationed) torpor patterns displayed by Peromyscus maniculatus, the deermouse. The proposal also seeks to determine the role that the endogenous opiates, in particualr B-endorphin (BE), play in modulating stress induced torpor. Information on the opiates will be obtained through IP administration of naloxone and through intraventricular administration of BE during different stages of the torpor/awake cycle. The role of the monoamines in modulating torpor will be determined through the use of specific monoamine agonists and antagonists. HPLC analyses of hypothalamic monoamine concentrations will be used to characterize the temporal dynamics and functional relationships of the metabolism of these monoamines with respect to torpor. The role of the suprachiasmatic nucleus (SCN) in the regulation of the timing of daily torpor will also be determined through the use of lesions and blockage of monoamine metabolism in the SCN.